Display device having a multilayered undercoating layer of silicon oxide and silicon nitride

ABSTRACT

According to one embodiment, a display device includes an underlying insulation layer formed on a surface of a resin layer, and a thin-film transistor formed above the surface of the resin layer via the underlying insulation layer. The underlying insulation layer includes a three-layer multilayer structure of a first silicon oxide film, a silicon nitride film formed above the first silicon oxide film, and a second silicon oxide film formed above the silicon nitride film.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2013-216298, filed Oct. 17, 2013, theentire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a display device.

BACKGROUND

By virtue of such advantageous features as light weight, small thicknessand low power consumption, flat-panel display devices, such as anorganic electroluminescence (EL) display device and a liquid crystaldisplay device, have been used in various fields of OA (officeautomation) equipment, information terminals, timepieces, and televisionreceivers. In particular, by virtue of high responsivity, displaydevices using thin-film transistors (TFTs) are widely used as monitorsof mobile terminals, computers, etc., which display a great deal ofinformation.

In recent years, as regards mobile information terminal devices such asmobile phones and PDAs (personal digital assistants), there has been anincreasing demand for a display device having a less thickness and aless weight, from the standpoint of design and portability, as well asperformance. For example, display devices, which realize thinnerstructures, have been proposed. As a method of realizing a lessthickness and less weight, there is known a technique wherein a resinlayer formed of a polyimide with a relatively high heat resistance, or aplastic substrate, is used in place of a glass substrate. When a resinlayer is formed of a polyimide, a resin layer using a polyimide isformed on a glass substrate. After TFTs, etc. are formed on the resinlayer, the resultant structure is divided into cells, and at last theresin layer is peeled from the glass substrate. Thereby, the resin layercan be formed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view which schematically illustrates adisplay device of a first embodiment.

FIG. 2 is a cross-sectional view which schematically illustrates a partof the display device in a manufacturing process of the display device,

FIG. 2 illustrating a state in which a resin layer, an underlyinginsulation layer and an a-Si layer are stacked on a glass substrate.

FIG. 3 is a view showing, in a table, evaluation objects and minimumbend R in Examples 1 to 4 of a second embodiment and ComparativeExamples 1 to 3.

FIG. 4 is a cross-sectional view illustrating a jig of the secondembodiment, FIG. 4 also illustrating a multilayer member of a resinlayer, an underlying insulation layer and an a-Si layer.

FIG. 5 is a cross-sectional view which schematically illustrates a partof a display device of a third embodiment, FIG. 5 illustrating a glasssubstrate, a resin layer and a first silicon oxide film.

DETAILED DESCRIPTION

In general, according to one embodiment, there is provided a displaydevice comprising: an underlying insulation layer formed on a surface ofa resin layer; and a thin-film transistor formed above the surface ofthe resin layer via the underlying insulation layer. The underlyinginsulation layer includes a three-layer multilayer structure of a firstsilicon oxide film, a silicon nitride film formed above the firstsilicon oxide film, and a second silicon oxide film formed above thesilicon nitride film.

To begin with, the basic concept of embodiments of the invention isdescribed.

A display device is formed, for example, by forming a TFT (thin-filmtransistor) above a glass substrate or a resin layer. An undercoatinglayer is provided between the glass substrate or resin layer and theTFT. The undercoating layer is provided in order to preventcontamination of the TFT (diffusion of impurities from the glasssubstrate or resin layer into the TFT). In addition, the undercoatinglayer is an underlying insulation layer and is electrically isolatedfrom the TFT.

For example, in the case of forming the display device by using theglass substrate and forming the TFT by using Si (silicon), theundercoating layer is formed, for example, on the glass substrate, andthe TFT is formed above the glass substrate via the undercoating layer.The undercoating layer includes a two-layer multilayer structure, andincludes a SiN_(X) film (silicon nitride film) and a SiO₂ film (siliconoxide film). The SiN_(X) film is formed on the glass substrate, and theSiO₂ film is formed on the SiN_(X) film. Since SiN_(X) and SiO₂ areinorganic materials, for example, the SiN_(X) film and SiO₂ film areformed by using a plasma CVD (chemical vapor deposition) method.

The advantage and disadvantage of the SiN_(X) film are described below.

Advantage: Since the SiN_(X) film has excellent ion blocking properties,contamination of the TFT can be prevented.

Disadvantage: In a case where a Si layer is formed immediately above theSiN_(X) film, there is a case in which the electrical characteristics ofthe TFT are adversely affected and the use of the TFT as a switchingelement becomes difficult. The reason for this is that when the Si layeris made polycrystalline, nitrogen atoms (excess nitrogen) of structuralelements of the SiN_(X) film are supplied into the Si layer. Since theabove has the same function as an N-type dopant, the Si layer isundesirably made to have a function of discharging electrons. In otherwords, nitrogen atoms function as donors in the Si layer, and anelectric current tends to easily flow when an electric current is not tobe caused to flow. Furthermore, in other words, even in the condition inwhich the channel region of the Si layer has to be made to have highresistance, a leak current flowing in the channel region increases.

Next, the advantages and disadvantage of the SiO₂ film are described.

Advantage 1: The affinity with the Si layer is excellent.

Advantage 2: The effect at a time of impurity doping is small.

Advantage 3: The supply of nitrogen atoms (excess nitrogen) from theSiN_(X) film to the Si layer can be prevented.

Disadvantage: The contribution to the prevention of contamination of theTFT is poor.

Next, a description is given of a manufacturing method for forming anundercoating layer and a TFT using p-Si (polysilicon) on a glasssubstrate.

In this case, the undercoating layer and a-Si (amorphous silicon) layerare, in many cases, formed at the same opportunity. For example, in thesame CVD reaction chamber in which the temperature of a glass substrateis about 400° C., three layers, namely a SiN_(X) film, a SiO₂ film andan a-Si layer, are successively formed in order on the glass substrateby only switching supply gases. The SiN_(X) film is formed on the glasssubstrate by plasma decomposition of a mixture gas of SiH₄ gas and NH₃gas. The SiO₂ film is formed on the SiN_(X) film by plasma decompositionof a mixture gas of SiH₄ gas and N₂O gas. The a-Si layer is formed onthe SiO₂ film by plasma decomposition of SiH₄ gas. Subsequently, anordinary fabrication process of a TFT using low-temperature p-Si will beperformed.

As has been described above, when the TFT is formed above the glasssubstrate, the undercoating layer is formed of two layers, namely theSiN_(X) film and SiO₂ film. Thereby, a display device with excellentproduct reliability can be obtained.

In the meantime, among display devices, a display device including, inplace of the glass substrate, a substrate formed of a material with goodflexibility has been developed. This aims at obtaining a display devicewhich is excellent in product reliability and is excellent inflexibility (i.e. is hardly crackable). Furthermore, this display deviceis advantageous, for example, in that the product design is notrestricted, unlike a display device including a glass substrate.

In general, there are the following two kinds of fabrication methods ofthe substrate with excellent flexibility.

(1) A plastic substrate (resin substrate) is used in place of the glasssubstrate.

(2) A resin layer (e.g. a resin layer using a polyimide) is formed onthe glass substrate, and the resin layer is peeled from the glasssubstrate. Thereby, this resin layer is used in place of the glasssubstrate.

In addition, also in the case of forming the display device by using theplastic substrate or resin layer, the undercoating layer is formed onthe plastic substrate or resin layer in order to prevent contaminationof the TFT. The TFT is formed above the plastic substrate or resin layervia the undercoating layer. Besides, in this case, it can be thoughtthat the undercoating layer is formed of two layers, namely a SiN_(X)film and a SiO₂ film. The SiN_(X) film is formed on the surface of theresin layer (the surface of the plastic substrate or the surface of theresin layer), and the SiO₂ film is formed on the SiN_(X) film.

However, when the SiN_(X) film is formed on the surface of the resinlayer as described above, such a problem arises that the resin layer (inparticular, a surface of the resin layer) changes in quality. The changein quality, in this context, means that the resin layer is hardened andthe flexibility (softness) of the resin layer is lost. If the resinlayer changes in quality, the resin layer becomes fragile and a crack(brittle fracture) tends to easily occur. Thus, even if the displaydevice is formed by replacing glass with resin, it is difficult toobtain the display device having excellent flexibility.

The reason for this is that when the SiN_(X) film is formed, the surfaceof the resin layer, which is heated up to a high temperature of about400° C., is exposed to NH₃ gas having a high reducing property.Incidentally, even when the SiN_(X) film was formed without using NH₃gas, a change in quality occurred in the resin layer (the surface of theresin layer). For example, even if the SiN_(X) film is formed by plasmadecomposition of a mixture gas of SiH₄ gas and N₂ gas, a change inquality occurs in the resin layer (the surface of the resin layer). Inaddition, even if the a-Si film is formed by plasma decomposition ofSiH₄ gas alone, a change in quality occurs in the resin layer (thesurface of the resin layer). From the above, it was understood that achange in quality occurs in the resin layer (the surface of the resinlayer) if the resin layer (the surface of the resin layer) is exposed toa reducing atmosphere.

As is understood from the above, in the above-described method offorming the undercoating layer (underlying insulation layer), it isdifficult to obtain a display device with excellent flexibility.

In the embodiment of the present invention, a display device withexcellent flexibility and product reliability can be obtained, so thatthe above problem can be solved. Next, the means and method for solvingthe above problem will be described.

Next, a display device of a first embodiment will be described in detailwith reference to the accompanying drawings. In the embodiment, anorganic EL display device is described as an example of a sheet-shapeddisplay device.

Incidentally, the disclosure is merely an example, and easilyconceivable proper changes within the spirit of the invention areincluded in the scope of the invention as a matter of course. Inaddition, in some cases, in order to make the description clearer, thewidths, thicknesses, shapes, etc. of the respective parts areschematically illustrated in the drawings, compared to the actual modes.However, the schematic illustration is merely an example, and adds norestrictions to the interpretation of the invention. In addition, in thespecification and drawings, the same elements as those described inconnection with preceding drawings are denoted by like referencenumerals, and a detailed description thereof is omitted unless otherwisenecessary.

As illustrated in FIG. 1, an organic EL display device DA adopts anactive matrix driving method, and includes an array substrate AR and acounter-substrate CT. The array substrate AR is formed by using a resinlayer 10. The array substrate AR includes switching elements SW1 to SW3and organic EL elements OLED1 to OLED3 above an inner surface 10A of theresin layer 10.

The resin layer 10 is an insulation layer, which is formed of, forexample, a material containing a polyimide (PI) as a main component. Theresin layer 10 has a thickness of, e.g. 5 to 30 μm. It is preferable touse, as the material of the resin layer 10, a material with a high heatresistance such as a polyamide-imide or polyaramide, as well as thepolyimide.

The inner surface 10A of the resin layer 10 is covered with anunderlying insulation layer 11 serving as a first insulation film.Specifically, the underlying insulation layer 11 is an undercoatinglayer, and is formed on the surface of the resin layer 10. Theunderlying insulation layer 11 functions as an inner surface barrierfilm for suppressing entrance of ionic impurities from the resin layer10 or entrance of moisture via the resin layer 10. The underlyinginsulation layer 11 is formed of an inorganic material, and is formedof, for example, a multilayer member of a SiN_(X) film (silicon nitridefilm) and a SiO₂ film (silicon oxide film). The underlying insulationlayer 11 may be formed by further including a SiON film (siliconoxynitride film). Incidentally, the underlying insulation layer 11 willbe described later in detail.

The switching elements SW1 to SW3 are formed on the underlyinginsulation layer 11. Specifically, the switching elements SW1 to SW3 areformed above the surface of the resin layer via the underlyinginsulation layer 11. These switching elements SW1 to SW3 are, forexample, TFTs (thin-film transistors) each including a semiconductorlayer SC as an active layer. The thickness of the semiconductor layer SCis, for example, 50 nm. The switching elements SW1 to SW3 have the samestructure. In the description below, attention is paid to the switchingelement SW1, and the structure thereof is described more specifically.

The switching element SW1 is of a top gate type, but this is merely anexample and a structure of a bottom gate type is not excluded. However,in the top gate type, since the semiconductor layer, in particular, apart thereof serving as a channel region, is put in direct contact withthe underlying insulation layer 11, the structure of the underlyinginsulation layer 11 illustrated in the present embodiment is moresuitable. In this embodiment, the semiconductor layer SC is formed ofp-Si. However, the semiconductor layer SC can be formed of a materialother than p-Si, and may be formed of a-Si or an oxide semiconductorformed of an oxide including at least one of indium (In), gallium (Ga)and zinc (Zn). The oxide semiconductor can be formed in a process atlower temperatures than the a-Si or p-Si. In particular, an oxidesemiconductor, such as IGZO, is preferable in that the investment costof manufacturing equipment can be reduced since a manufacturingapparatus, which is used for fabricating TFTs including a-Sisemiconductor layers, can also be used as such.

The semiconductor layer SC is formed on the underlying insulation layer11, and is covered with a second insulation film 12. The secondinsulation film 12 is a gate insulation film and is also disposed on theunderlying insulation layer 11. A gate electrode WG of the switchingelement SW1 is formed on the second insulation film 12. The gateelectrode WG is covered with a third insulation film 13. The thirdinsulation film 13 is also disposed on the second insulation film 12.

A source electrode WS and a drain electrode WD of the switching elementSW1 are formed on the third insulation film 13. The source electrode WSand drain electrode WD are put in contact with the semiconductor layerSC. The source electrode WS and drain electrode WD are covered with afourth insulation film 14. The fourth insulation film 14 is alsodisposed on the third insulation film 13.

The organic EL elements OLED1 to OLED3 are formed on the fourthinsulation film 14. In the example illustrated, the organic EL elementOLED1 is electrically connected to the switching element SW1, theorganic EL element OLED2 is electrically connected to the switchingelement SW2, and the organic EL element OLED3 is electrically connectedto the switching element SW3.

The color of emission light of each of the organic EL elements OLED1 toOLED3 is white. In addition, each of the organic EL elements OLED1 toOLED3 is configured as a top emission type which emits light toward thecounter-substrate CT. The organic EL elements OLED1 to OLED3 have thesame structure.

The organic EL element OLED1 includes an anode PE1 which is formed onthe fourth insulation film 14. The anode PE1 is in contact with thedrain electrode WD of the switching element SW1 and is electricallyconnected to the switching element SW1. Similarly, the organic ELelement OLED2 includes an anode PE2 which is electrically connected tothe switching element SW2, and the organic EL element OLED3 includes ananode PE3 which is electrically connected to the switching element SW3.The anodes PE1 to PE3 may be formed of, for example, a transparent,electrically conducive material such as indium tin oxide (ITO) or indiumzinc oxide (IZO), or may be formed of a metallic material such asaluminum (Al), magnesium (Mg), silver (Ag), titanium (Ti), or an alloythereof, or a multilayer material thereof. In the case of the topemission type, it is desirable that the anodes PE1 to PE3 be formed of ametallic material with a high reflectivity.

The organic EL elements OLED1 to OLED3 further include an organic lightemission layer ORG and a cathode CE. The organic light emission layerORG is located on the anodes PE1 to PE3. The organic light emissionlayer ORG is continuously formed, without a break, over the organic ELelements OLED1 to OLED3. The cathode CE is located on the organic lightemission layer ORG. In addition, the cathode CE is continuously formed,without a break, over the organic EL elements OLED1 to OLED3. Thecathode CE is formed of, for example, a transparent, electricallyconductive material such as ITO or IZO.

Specifically, the organic EL element OLED1 is composed of the anode PE1,organic light emission layer ORG and cathode CE. Similarly, the organicEL element OLED2 is composed of the anode PE2, organic light emissionlayer ORG and cathode CE, and the organic EL element OLED3 is composedof the anode PE3, organic light emission layer ORG and cathode CE.

In the organic EL elements OLED1 to OLED3, a hole-injection layer or ahole-transport layer may be further provided between each of the anodesPE1 to PE3 and the organic light emission layer ORG, and anelectron-injection layer or an electron-transport layer may be furtherprovided between the organic light emission layer ORG and the cathodeCE.

The organic EL elements OLED1 to OLED3 are partitioned by ribs 15. Theribs 15 are formed on the fourth insulation film 14 and cover the edgesof the anodes PE1 to PE3. Although not described in detail, the ribs 15are formed, for example, in a grid shape or in a stripe shape on thefourth insulation film 14. The ribs 15 are covered with the organiclight emission layer ORG. Specifically, the organic light emission layerORG extends over not only the anodes PE1 to PE3 but also over the ribs15.

The counter-substrate CT is formed by using a transparent resin layer30. The counter-substrate CT includes a first color filter 31, a secondcolor filter 32 and a third color filter 33 above an inner surface 30Aof the resin layer 30.

The resin layer 30 is a transparent insulative substrate, which isformed of, for example, a material containing a polyimide (PI) as a maincomponent. The resin layer 30 has a thickness of, e.g. 5 to 30 μm. Asthe material of the resin layer 30, the same material as the resin layer10 is applicable. In particular, since light emitted from thetop-emission type organic EL elements OLED1 to OLED3 passes through theresin layer 30, it is desirable that the resin layer 30 be formed of amaterial with high transparency.

The first color filter 31 is opposed to the organic EL element OLED1 andpasses a light component of a blue wavelength of white light. The secondcolor filter 32 is opposed to the organic EL element OLED2 and passes alight component of a green wavelength of white light. The third colorfilter 33 is opposed to the organic EL element OLED3 and passes a lightcomponent of a red wavelength of white light. A boundary between thefirst color filter 31 and second color filter 32, a boundary between thesecond color filter 32 and third color filter 33 and a boundary betweenthe first color filter 31 and third color filter 33 are located abovethe ribs 15.

The array substrate AR and counter-substrate CT are attached by atransparent adhesive 40. Specifically, the adhesive 40 is interposedbetween the organic EL element OLED1 and first color filter 31, betweenthe organic EL element OLED2 and second color filter 32 and between theorganic EL element OLED3 and third color filter 33. In the meantime, abarrier film (sealing film), which protects the organic EL elementsOLED1 to OLED3 from contaminants such as moisture, oxygen and hydrogen,may be disposed between the cathode and the adhesive 40.

According to the organic EL display device DA, when each of the organicEL elements OLED1 to OLED3 has emitted light, this radiated light (whitelight) is emitted to the outside through the first color filter 31,second color filter 32 or third color filter 33. At this time, a lightcomponent of a blue wavelength of the white light, which has beenradiated from the organic EL element OLED1, passes through the firstcolor filter 31. In addition, a light component of a green wavelength ofthe white light, which has been radiated from the organic EL elementOLED2, passes through the second color filter 32. A light component of ared wavelength of the white light, which has been radiated from theorganic EL element OLED3, passes through the third color filter 33.Thereby, color display is realized.

Next, the underlying insulation layer 11 is described in detail.

As illustrated in FIG. 2, the underlying insulation layer 11 is formedon the surface of the resin layer 10. The underlying insulation layer 11includes a three-layer multilayer structure of a first silicon oxidefilm 1, a silicon nitride film 2 and a second silicon oxide film 3. Inthis embodiment, the underlying insulation layer 11 is formed of thesethree layers alone.

The first silicon oxide film 1 is formed on the surface of the resinlayer 10 by using SiO₂. Thus, in the underlying insulation layer 11, thelayer that is in contact with the resin layer 10 is the first siliconoxide film 1. The thickness of the first silicon oxide film 1 is, forexample, 50 nm.

The silicon nitride film 2 is formed above the first silicon oxide film1 by using SiN_(X). In this embodiment, the silicon nitride film 2 isformed on the first silicon oxide film 1. The thickness of the siliconnitride film 2 is, for example, 50 nm.

The second silicon oxide film 3 is formed above the silicon nitride film2 by using SiO₂. In this embodiment, the second silicon oxide film 3 isformed on the silicon nitride film 2. Thus, in the underlying insulationlayer 11, the layer that is in contact with the semiconductor layer SC,which functions as the active layer of the switching element (TFT), isthe second silicon oxide film 3. The thickness of the second siliconoxide film 3 is, for example, 300 nm.

Next, a description is given of an example of a method of manufacturingthe organic EL display device DA of the present embodiment.

As illustrated in FIG. 2, to start with, a glass substrate 100 isprepared as a support substrate. Subsequently, the glass substrate 100is washed (brush washing). Then, a polyimide precursor compound, whichis a varnish-like composition, is coated with a thickness of 5 to 30 μmon the glass substrate 100 (slit coating) by using a film-forming devicesuch as a slit coater. Thereafter, the polyimide precursor compound iscured by heat treatment at 480° C. for one hour. Thus, a resin layer 10is formed.

Following the above, the glass substrate 100, on which the resin layer10 is formed, is placed in a reaction chamber of a parallel-plate-typeplasma CVD apparatus. Then, in a state in which the temperature of theglass substrate 100 is about 400° C., four layers, namely a firstsilicon oxide film 1 with a thickness of 50 nm, a silicon nitride film 2with a thickness of 50 nm, a second silicon oxide film 3 with athickness of 300 nm and an a-Si layer 5 with a thickness of 50 nm, aresuccessively formed in order on the glass substrate 100, while supplygases into the reaction chamber are being switched.

The first silicon oxide film 1 is formed on the resin layer 10 by plasmadecomposition of a mixture gas of SiH₄ gas and N₂O gas. The siliconnitride film 2 is formed on the first silicon oxide film 1 by plasmadecomposition of a mixture gas of SiH₄ gas and NH₃ gas. The secondsilicon oxide film 3 is formed on the silicon nitride film 2 by plasmadecomposition of a mixture gas of SiH₄ gas and N₂O gas. The a-Si layer 5is formed on the second silicon oxide film 3 by plasma decomposition ofSiH₄ gas.

From the above, the above-described four layers can be successivelyformed by continuing to flow SiH₄ gas, and switching the sub-gases.Thus, with the tact time being hardly increased, the underlyinginsulation layer 11 (underlying insulation layer 11 and a-Si layer 5)can be formed.

Thereafter, the a-Si layer 5 is patterned, the patterned a-Si isirradiated with a laser beam, etc., and the a-Si is polycrystallized.Incidentally, it is advantageous that the amount of hydrogen in the a-Silayer 5 is small, since no bumping or the like will occur. Normally, ina heating step after the film formation, hydrogen is discharged to theoutside of the a-Si layer 5. If the tact time is taken into account, itis better that the initial amount of hydrogen is small. Thus, it isdesirable that the a-Si layer 5 be formed at as high as possibletemperatures.

As illustrated in FIG. 1 and FIG. 2, subsequently, by using p-Si formedon the underlying insulation layer 11, switching elements SW1 to SW3 areformed on the underlying insulation layer 11 through an ordinary TFTfabrication process using low-temperature p-Si. In addition, on theunderlying insulation layer 11, not only the switching elements, butalso a second insulation film 12, a third insulation film 13 and afourth insulation film 14 are formed, and at the same time variouswirings are formed.

Then, on the fourth insulation film 14, organic EL elements OLED1 toOLED3 are formed. Specifically, after anodes PE1 to PE3 are formed onthe fourth insulation film 14, ribs 15 are formed, and an organic lightemission layer ORG and a cathode CE are formed. Where necessary, asealing film is formed on the organic EL elements OLED1 to OLED3.

On the other hand, although not illustrated, a glass substrate, which isdifferent from the above-described glass substrate 100, is prepared as asupport substrate. Subsequently, the glass substrate is washed. Then, apolyimide precursor compound, which is a varnish-like composition, iscoated with a thickness of 5 to 30 μm on the glass substrate by using afilm-forming device such as a slit coater. Thereafter, the polyimideprecursor compound is cured by heat treatment, and a resin layer 30 isformed.

Subsequently, a first color filter 31, a second color filter 32 and athird color filter 33 are formed on the resin layer 30. Thereafter, anadhesive 40 is coated on the surfaces of the first to third colorfilters 31 to 33.

Next, the glass substrate 100 and the glass substrate, on which thefirst to third color filters 31 to 33 are formed, are attached.Specifically, the surface of the array substrate AR on that side, onwhich the organic EL elements OLED1 to OLED3 are located, and thesurface of the counter-substrate CT on that side, on which the first tothird color filters 31 to 33 are located, are bonded by the adhesive 40.

Thereafter, the glass substrate 100 is peeled from the resin layer 10,and the other glass substrate is peeled from the resin layer 30, thusremoving the two glass substrates.

Thereby, the organic EL display device DA of the present embodiment ismanufactured.

According to the organic EL display device DA of the first embodimentwith the above-described structure, the organic EL display device DAcomprises the underlying insulation layer 11 formed on the surface ofthe resin layer 10, and the switching elements SW1 to SW3 formed abovethe surface of the resin layer 10 via the underlying insulation layer11.

The underlying insulation layer 11 includes the first silicon oxide film1. In the underlying insulation layer 11, the first silicon oxide film 1is in contact with the resin layer 10. When the first silicon oxide film1 is formed, since the mixture gas including N₂O gas is supplied intothe reaction chamber, the surface of the resin layer 10, which is heatedat a high temperature of about 400° C., is hardly exposed to a reducingatmosphere. Thereby, a change in quality of the resin layer 10 (inparticular, the surface of the resin layer 10) can be reduced, and theflexibility of the resin layer 10 can be maintained.

The underlying insulation layer 11 includes the silicon nitride film 2formed above the first silicon oxide film 1. When the silicon nitridefilm 2 is formed, since the resin layer 10 is covered with the firstsilicon oxide film 1, the flexibility of the resin layer 10 can bemaintained. Since the silicon nitride film 2 has an excellention-blocking property, contamination of the switching elements SW1 toSW3 (the semiconductor layers SC) can be prevented.

The underlying insulation layer 11 includes the second silicon oxidefilm 3 formed above the silicon nitride film 2. In the underlyinginsulation layer 11, the second silicon oxide film 3 is in contact withthe active layers (semiconductor layers SC) of the switching elementsSW1 to SW3. The semiconductor layer SC is provided, not immediatelyabove the silicon nitride film 2, but above the silicon nitride film 2via the second silicon oxide film 3. The second silicon oxide film 3 canprevent supply of nitrogen atoms (excess nitrogen) from the siliconnitride film 2 into the semiconductor layer SC. Thereby, it becomespossible to prevent an adverse effect on the electrical characteristicsof the switching elements SW1 to SW3 (semiconductor layers SC).

From the above, the organic EL display device DA with excellentflexibility and product reliability can be obtained.

Next, a display device of a second embodiment is described. In thisembodiment, the same functional parts as in the above-described firstembodiment are denoted by like reference numerals, and a detaileddescription thereof is omitted.

As illustrated in FIG. 3 and FIG. 2, in this embodiment, organic ELdisplay devices DA of Examples 1 to 4 are described.

EXAMPLE 1

The organic EL display device DA of Example 1 is formed like the organicEL display device DA of the first embodiment. Incidentally, thethickness of the first silicon oxide film 1 is 50 nm.

EXAMPLE 2

The organic EL display device DA of Example 2 is formed like the organicEL display device DA of the first embodiment, except for the thicknessof the first silicon oxide film 1. Incidentally, the thickness of thefirst silicon oxide film 1 is 10 nm.

EXAMPLE 3

The organic EL display device DA of Example 3 is formed like the organicEL display device DA of the first embodiment, except for the thicknessof the first silicon oxide film 1. Incidentally, the thickness of thefirst silicon oxide film 1 is 30 nm.

EXAMPLE 4

The organic EL display device DA of Example 4 is formed like the organicEL display device DA of the first embodiment, except for the thicknessof the first silicon oxide film 1. Incidentally, the thickness of thefirst silicon oxide film 1 is 100 nm.

Next, the flexibility of each of the organic EL display devices DA ofExamples 1 to 4 is evaluated. In this embodiment, the evaluation of theflexibility was conducted at a stage at which the organic EL displaydevice DA was fabricated halfway up to a fabrication step (i.e.formation of a-Si layer 5). The reason for this is that the evaluationof the flexibility is sufficient if the manufacturing process progressesto this stage. In addition, for the purpose of comparison with theflexibility of each of the organic EL display devices DA of Examples 1to 4, the flexibility of each of organic EL display devices ofComparative Examples 1 to 3 was also evaluated.

In Examples 1 to 4, at a time point when the multilayer member of theresin layer 10, underlying insulation layer 11 and a-Si layer 5 wasformed on the glass substrate 100, the glass substrate 100 was peeledfrom the resin layer 10, and the flexibility of the taken-out multilayermember was evaluated.

In Comparative Example 1, at a time point when the resin layer 10 of theabove-described first embodiment was formed on the glass substrate 100,the glass substrate 100 was peeled from the resin layer 10, and theflexibility of the taken-out resin layer 10 alone was evaluated.

In Comparative Example 2, at a time point when the multilayer member ofthe resin layer 10 and second silicon oxide film 3 of theabove-described first embodiment was formed on the glass substrate 100,the glass substrate 100 was peeled from the resin layer 10, and theflexibility of the taken-out multilayer member was evaluated.Incidentally, the multilayer member of Comparative Example 2 is formedwithout the first silicon oxide film 1 and silicon nitride film 2.

In Comparative Example 3, at a time point when the multilayer member ofthe resin layer 10, silicon nitride film 2, second silicon oxide film 3and a-Si layer 5 of the above-described first embodiment was formed onthe glass substrate 100, the glass substrate 100 was peeled from theresin layer 10, and the flexibility of the taken-out multilayer memberwas evaluated. Incidentally, the multilayer member of ComparativeExample 3 is formed without the first silicon oxide film 1.

Next, a description is given of a jig which is used for the evaluationof an evaluation object such as the above-described multilayer member.

As illustrated in FIG. 4, a jig 200 includes a pair of rods 201, 202.The rods 201 and 202 are provided in parallel with a predeterminedinterval. The cross-sectional shape of the rod 201, 202 is a circle(perfect circle). The interval between the rods 201 and 202 isadjustable, and may be adjusted such that the evaluation object isfixed, or such that the evaluation object can be passed between the rods201 and 202. In addition, as the rods 201 and 202, a plurality of kindsof rods with different diameters may be changed and used. In the presentcase, the diameter of the rod 201, 202 is 2 R.

When the flexibility of the evaluation object is evaluated by using thejig 200 illustrated in FIG. 4, the evaluation object is inserted betweenthe rods 201 and 202, and the evaluation object is clamped and fixedbetween the rods 201 and 202. Then, the evaluation object is bent by180°, and a minimum bend radius of the evaluation object at a time whenno plastic deformation occurred in the evaluation object is defined as aminimum bend R. Based on the value of the minimum bend R, theflexibility of the evaluation object is evaluated.

In addition, when the minimum bend R is evaluated (measured), theevaluation is performed by applying an initial stress F in an upwarddirection or a downward direction in the Figure. When a downward minimumbend R is evaluated, the evaluation object can be bent downward by 180°by putting the evaluation object in close contact with half theperiphery of the rod 201 by, for example, applying a downward initialstress F. Similarly, when an upward minimum bend R is evaluated, theevaluation object can be bent upward by 180° by putting the evaluationobject in close contact with half the periphery of the rod 202 by, forexample, applying an upward initial stress F. At this time, by graduallydecreasing the diameter of the rod 201, 202 and evaluating (inspecting)the presence/absence of plastic deformation in the evaluation object,the minimum bend R can be found.

As shown in FIG. 3, the minimum bend R of the multilayer member of eachof Examples 1 to 4 was at least 2 mm in each of the downward directionand upward direction. Thereby, it was understood that the multilayermember of each of Examples 1 to 4 was excellent in flexibility.

In addition, the minimum bend R of each of the resin layer 10 ofComparative Example 1 and the multilayer member of Comparative Example 2was at least 2 mm in each of the downward direction and upwarddirection. From this, it was understood that each of the resin layer 10of Comparative Example 1 and the multilayer member of ComparativeExample 2 was excellent in flexibility.

However, in the multilayer member of Comparative Example 3, the downwardminimum bend R was 25 mm and the upward minimum bend R was 30 mm. Fromthis, it is understood that the flexibility of the multilayer member ofComparative Example 3 is lost. In addition, from the fact that theupward minimum bend R is greater than the downward minimum bend R, it isunderstood that the resin layer 10 (in particular, the surface of theresin layer 10) changed in quality and the flexibility of the resinlayer 10 was lost.

According to the organic EL display device DA of the second embodimentwith the above-described structure, the organic EL display device DAcomprises the underlying insulation layer 11 formed on the surface ofthe resin layer 10, and the switching elements SW1 to SW3. Theunderlying insulation layer 11 includes the first silicon oxide film 1,silicon nitride film 2 and second silicon oxide film 3.

Not only in the case where the thickness of the first silicon oxidelayer 1 is 50 nm, but also in the case where the thickness is any one of10 nm, 30 nm and 100 nm, the flexibility of the resin layer 10 can bemaintained. Thus, in order to maintain the flexibility of the resinlayer 10 (organic EL display device DA), it is preferable that thethickness of the first silicon oxide film 1 is 10 nm or more, and 100 nmor less.

Incidentally, in order to maintain the flexibility of the resin layer 10(organic EL display device DA), the thickness of the first silicon oxidefilm 1 may exceed 100 nm. However, as the first silicon oxide film 1becomes thicker, this leads to an increase in time of film formation andloss of uniformity in thickness.

Besides, in the second embodiment, the same advantageous effects as inthe first embodiment can be obtained.

From the above, the organic EL display device DA with excellentflexibility and product reliability can be obtained.

Next, a display device of a third embodiment is described. In thisembodiment, the same functional parts as in the above-described firstembodiment are denoted by like reference numerals, and a detaileddescription thereof is omitted.

As illustrated in FIG. 5, the organic EL display device DA is formedlike the above-described first embodiment. When the organic EL displaydevice DA is manufactured, a first silicon oxide film 1 is formed so asto completely cover the resin layer 10.

Incidentally, although not illustrated, not only the first silicon oxidefilm 1, but all of the first silicon oxide film 1, silicon nitride film2 and second silicon oxide film 3 are formed so as to completely coverthe resin layer 10. A peripheral edge portion of the first silicon oxidefilm 1 is located on the glass substrate 100 and adhered to the glasssubstrate 100. The first silicon oxide film 1 is provided on the glasssubstrate 100 such that a predetermined distance (e.g. several mm) isprovided between the outer peripheral edge of the first silicon oxidefilm 1 and the outer peripheral edge of the glass substrate 100.

According to the organic EL display device DA of the third embodimentwith the above-described structure, the organic EL display device DAcomprises the underlying insulation layer 11 formed on the surface ofthe resin layer 10, and the switching elements SW1 to SW3. Theunderlying insulation layer 11 includes the first silicon oxide film 1,silicon nitride film 2 and second silicon oxide film 3. The organic ELdisplay device DA of the third embodiment is formed like the organic ELdisplay device DA of the above-described first embodiment. Thus, in thethird embodiment, the same advantageous effects as in the firstembodiment can be obtained.

The first silicon oxide film 1 is formed so as to completely cover theresin layer 10. Thus, a change in quality can be reduced also at theperipheral edge part of the resin layer 10.

The peripheral edge part of the first silicon oxide film 1 is located onthe glass substrate 100. SiO₂ is excellent in adhesivity to glass. Thus,undesired peeling of the resin layer 10 from the glass substrate 100 canbe reduced in the manufacturing process.

The first silicon oxide film 1 is formed such that a predetermineddistance is provided between the outer peripheral edge of the firstsilicon oxide film 1 and the outer peripheral edge of the glasssubstrate 100. It is thus possible to reduce the occurrence of peeledmatter (waste matter) of the first silicon oxide film 1, etc., whichtends to easily occur when the first silicon oxide film 1, etc. areformed up to the outer peripheral edge of the glass substrate 100 or thevicinity of the outer peripheral edge.

From the above, the organic EL display device DA with excellentflexibility and product reliability can be obtained.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions.

For example, the thickness of the second silicon oxide film 3 is notlimited to 300 nm, and can be variously changed. In order to avoid anadverse effect on the electrical characteristics of the switchingelements SW1 to SW3 (semiconductor layers SC), it is preferable that thethickness of the second silicon oxide film 3 is 100 nm or more, and 500nm or less. In addition, the second silicon oxide film 3 is irradiatedwith a laser beam, or is heated. From the above, too, it is preferablethat the thickness of the second silicon oxide film 3 is 100 nm or more.

In the meantime, the thickness of the second silicon oxide film 3 may beless than 100 nm. However, as the second silicon oxide film 3 becomesthinner, an adverse effect tends to be easily occur on the electricalcharacteristics of the switching elements SW1 to SW3 (semiconductorlayers SC).

In addition, the thickness of the second silicon oxide film 3 may exceed500 nm. However, as the second silicon oxide film 3 becomes thicker,this leads to an increase in time of film formation and loss ofuniformity in thickness.

If the underlying insulation layer 11 includes the three-layermultilayer structure of the first silicon oxide film 1 which is incontact with the resin layer 10, the silicon nitride film 2 formed abovethe first silicon oxide film 1, and the second silicon oxide film 3which is formed above the silicon nitride film 2 and is in contact withthe active layers (semiconductor layers SC) of the switching elementsSW1 to SW3, the above-described advantageous effects can be obtained.Thus, in the underlying insulation layer 11, the above-described threelayers may not be successively stacked and formed. For example, theunderlying insulation layer 11 may be formed of the first silicon oxidefilm 1, the silicon nitride film 2 formed on the first silicon oxidefilm 1, another proper film (e.g. silicon oxynitride film) formed on thesilicon nitride film 2, and the second silicon oxide film 3 formed onthe another proper film.

It should suffice if the underlying insulation layer 11 is formed on aresin layer surface, such as the surface of the resin layer 10. Forexample, the organic EL display device DA may further include a glasssubstrate 100. In this case, the organic EL display device DA may beformed without peeling the resin layer 10 from the glass substrate 100.Besides, the organic EL display device DA may include a plasticsubstrate (resin substrate) in place of the resin layer 10. In thiscase, it should suffice if the underlying insulation layer 11 is formedon the surface of the plastic substrate.

The semiconductor layer SC may be formed of a semiconductor materialother than p-Si. For example, the semiconductor layer SC may be formedof a-Si.

The colors of emission lights of the organic EL elements OLED1 to OLED3are not limited to white, and may be, for instance, red, green and blue.In this case, the organic EL display device DA can emit (display) redlight, green light and blue light, without the first color filter 31,second color filter 32 and third color filter 33.

The embodiments of the present invention are not limited to theapplication to the above-described organic EL display device DA. Theembodiments are also applicable to other organic EL display devices(e.g. a bottom-emission-type organic EL display device, and an organicEL device in which light emission layers of RGB are formed by selectivecoating), or display devices (e.g. a display device using a liquidcrystal element, or an electrophoresis element) other than organic ELdisplay devices. For example, the self-luminous element is not limitedto a diode (organic EL diode), and use may be made of various displayelements which are configured to be self-luminous. Needless to say, theabove-described embodiments are applicable to display devices rangingfrom small/middle-sized display devices to large-sized display devices,without particular restrictions.

What is claimed is:
 1. A display device comprising: an underlyinginsulation layer formed on an upper surface of a resin layer; and athin-film transistor comprising an active layer which is formed abovethe upper surface of the resin layer, wherein the underlying insulationlayer consists of a three-layer multilayer structure of a first siliconoxide film, a silicon nitride film formed above the first silicon oxidefilm, and a second silicon oxide film formed above the silicon nitridefilm, wherein in the underlying insulation layer the first silicon oxidefilm is in contact with the resin layer and the second silicon oxidefilm is in contact with the active layer of the thin-film transistor,and wherein the upper surface of the resin layer and a peripheralsurface of the resin layer, but not a bottom surface of the resin layer,are covered with the first silicon oxide film.
 2. The display device ofclaim 1, wherein the active layer is formed of polysilicon.
 3. Thedisplay device of claim 1, wherein the first silicon oxide film has athickness of 10 nm or more, and 100 nm or less.
 4. The display device ofclaim 1, wherein the second silicon oxide film has a thickness of 100 nmor more, and 500 nm or less.
 5. The display device of claim 1, whereinthe resin layer comprises a polyimide.
 6. The display device of claim 1,wherein the resin layer comprises a polyamide-imide or a polyaramide. 7.The display device of claim 1, wherein the resin layer has a thicknessof 5 to 30μm.
 8. The display device of claim 1, wherein the resin layerhas a thickness of 5 to 30 μm; the first silicon oxide film has athickness of 10 nm or more and 100 nm or less; and the second siliconoxide film has a thickness of 100 nm or more and 500 or less.
 9. Thedisplay device of claim 8, wherein the resin layer comprises apolyimide.
 10. The display device of claim 8, wherein the resin layercomprises a polyamide-imide or a polyaramide.
 11. The display device ofclaim 1, wherein the display device is prepared by a process comprisingforming the resin layer on a glass substrate, then covering the uppersurface of the resin layer and the peripheral surface of the resin layerwith the first silicon oxide film to form a covered resin layer, andpeeling the covered resin layer from the glass substrate.